| 摘要 |
A vehicle security system includes a transmitter unit 20 arranged to send coded signals to a security control unit 18 on the vehicle when its lock and unlock buttons 30, 32 are pressed. The transmitter unit includes a control circuit which is arranged to increase the power of the transmitted signals if the buttons 30, 32 are pressed repeatedly at more than a predetermined rate, or if they are held down for more than a predetermined time. This allows a low power initial signal to be used to maximise battery life, but a higher powered signal to be used if necessary to overcome interference or to operate the security system from large distances. |
